The present invention relates to control techniques and systems for generating mode transitions between grid-connected and standalone modes for microturbine generating systems. This field is unlike that comprising standard backup generators, such as diesel-driven generators, which typically have only two modes, on and off.
The present invention is of a system and method for controlling a microturbine generator system comprising: providing a computer control unit; providing a utility power grid sensor input line to the computer control unit; and providing a utility power grid disconnect command output line from the computer control unit; and causing, via the computer control unit, automatic transitions of the microturbine generator system between at least four states, the at least four states comprising a generator standby backup mode, a generator standalone mode, a transfer to standby backup mode, and a generator startup battery charging mode. In the preferred embodiment, the at least four states additionally comprises a transfer to standalone mode. A utility circuit breaker status input line to the computer control unit is also preferred. The computer control unit in causing a transition to generator standalone mode causes the generator to start, disconnects the load from the utility power grid and then connects the load to output from the generator. The computer control unit in causing a transition to transfer to standby backup mode causes the generator to enter a power-down sequence, disconnects the load from output from the generator, and connects the load to the utility power grid. The computer control unit in causing a transition to generator startup battery charging mode causes the generator to run, maintains disconnection of the load from output from the generator, and maintains connection of the load to the utility power grid. The computer control unit causes a transition to generator startup battery charging mode at periodic intervals. A contactor connects and disconnects the load from the utility power grid and is controlled by the utility power grid disconnect command output line. The contactor comprises an auxiliary contact for providing status of the contactor to the computer control unit via a utility grid disconnect relay status line. A utility grid disconnect-relay controls the contactor.